1. Field of the Invention
The present invention relates to a wafer holding member for use in a wafer prober for inspecting a semiconductor wafer and the wafer prober including the wafer holding member.
2. Description of the Background Art
Conventionally, inspection processes for a semiconductor wafer include processing of heating the semiconductor wafer which is a to-be processed object. The heating processing includes a burn-in process for heating the semiconductor wafer to a temperature higher than an usual usage temperature for acceleratingly degrading the qualities of semiconductor chips which may become defective products and eliminating such semiconductor chips, thereby preventing occurrence of defective products after shipment.
In the burn-in process, before the semiconductor wafer having circuit formed thereon is cut into the individual semiconductor chips, measurement of electric characteristics of the respective semiconductor chips are performed while the semiconductor wafer is kept heated and, thus, defective products are removed therefrom. There has been a strong need for reducing processing time of the burn-in process, in order to increase throughput.
The aforementioned burn-in process is performed using a heater unit for heating the semiconductor wafer, wherein the heater unit includes a wafer holding member for holding the semiconductor wafer. Conventional heater units employ a flat-plate shaped metal plate as the wafer holding member, since there is a need for bringing an entire back surface of the semiconductor wafer into contact with ground electrodes.
In the burn-in processing, the semiconductor wafer having the circuit formed thereon is placed on a wafer placing surface of the wafer holding member made of the metal plate, and measurement of the electric characteristics of the semiconductor chips is performed. During measurement of the electric characteristics of the semiconductor chips, a probing device including a large number of energizing probe pins, called a probe card, is pressed against the semiconductor wafer with a force in a range between several tens of kgf and several hundreds kgf. Accordingly, if the wafer holding member has a small thickness, the wafer holding member may be deformed, thereby causing poor contact between the semiconductor wafer and the probe pins. Therefore, in order to ensure rigidity of the wafer holding member, it has been necessary to employ a thick metal plate with a thickness of 15 mm or more as the wafer holding member, which has made it necessary to take a longer time period for raising and reducing the temperature of the semiconductor wafer. This has been such obstruction in increasing the throughput.
Further, in the burn-in process, an electric current is fed to the semiconductor chips for measurement of the electric characteristics thereof. Along with increase in outputs of the semiconductor chips in recent years, heat generation from the semiconductor chips during measurement of the electric characteristics thereof is increased, which may sometimes cause fractures of the semiconductor chips due to self heating thereof. Accordingly, there has been a need for rapidly cooling down the semiconductor chips after measurement of the electric characteristics thereof. Further, there is a need for uniformizing heat over the semiconductor chips during measurement of the electric characteristics and, therefore, copper (Cu) with a heat conductivity of 403 W/mK, namely with a high heat conductivity, has been employed as materials of the metal plates constituting the wafer holding members.
Japanese Patent Laying-Open No. 2001-033484 (Patent Document 1) suggests a wafer holding member constituted by a ceramic substrate with a small thickness but higher rigidity which is less prone to deformation and a thin metal layer formed on the surface of the ceramic substrate, instead of the wafer holding member made of the thick metal plate. Patent Document 1 describes that this wafer holding member causes no poor contact between the semiconductor wafer and the probe pins since it has higher rigidity and, also, the wafer holding member enables raising and reducing the temperature of the semiconductor wafer within shorter time periods since it has a smaller heat capacity. Further, Patent Document 1 describes that aluminum alloy and stainless steel can be employed as a supporting table for installing the wafer holding member thereon.
However, when the wafer holding member is supported only at its outermost periphery by the supporting table as described in Patent Document 1, the wafer holding member may be warped due to the pressing pressure of a probe card and, therefore, there has been a need for further contrivance such as supporting the wafer holding member with a plurality of supporting columns, in addition to the supporting table.
Further, in recent years, along with miniaturization of semiconductor processes, force applied to the semiconductor chip per unit area during probing has been increased and, also, there has been a need for higher accuracy in positioning the probe card and the wafer holding member. In general, the wafer holding member repeatedly performs operations of heating the semiconductor wafer to a predetermined temperature, moving to a predetermined position during probing, and pressing the probe card against the semiconductor wafer. At this time, in order to enable moving the wafer holding member to the predetermined position, a driving system therefor is required to have high accuracy.
However, when the semiconductor wafer is heated to the predetermined temperature, for example, temperature in a range of 100 to 200° C., heat thereof transfers to the driving system to cause thermal expansion of metal components constituting the driving system, thereby causing a problem of degradation in accuracy of the driving system. Further, due to increase in force applied during probing, the wafer holding member for placing the semiconductor wafer thereon is required to have rigidity, which has increased size and weight of the wafer holding member, thereby causing a problem of adverse influence by the increased weight on accuracy of the driving system. Further, along with the increase in size of the wafer holding member, there has been a need of significantly longer time periods for raising and reducing the temperature of the semiconductor wafer, thereby causing a problem of reduction in the throughput.
In order to reduce the time periods for raising and reducing the temperature of the semiconductor wafer to increase the throughput, the wafer holding member is provided with the cooling mechanism, in many cases. Conventional cooling mechanisms perform air cooling as described in, for example, Patent Document 1, and cooling plates made of metal are provided beneath the wafer holding members. However, the former case has a problem of a low cooling rate due to air cooling. The latter case has a problem that the cooling plate is prone to deformation since it is made of metal and the pressure by the probe card is directly applied to the cooling plate during probing.